Karthus The Deathsinger

Mid

3150

790

Death Defied

Upon dying, Karthus enters a spirit form, which allows him to continue casting spells for 7 seconds. During this time, his abilities cost no mana.

Lay Waste

Active: After a 0.5 second delay, Karthus blasts target area at the cursors position, dealing magic damage to every enemy in the area. The damage is doubled if it only hits one unit.
Cooldown: 1 second
Range to Center of AoE: 875
Radius of AoE: 50
Cost: 20/26/32/38/44 mana
Magic Damage (Multiple Target): 40/60/80/100/120 (+0.3 per ability power)
Magic Damage (Single Target): /80/120/160/200/240(+0.6 per ability power)

Toggle Off: When Karthus kills a unit, he restores mana.
Toggle On: Karthus surrounds himself with the souls of his victims, dealing magic damage per second for a high mana cost.
Radius of AoE: 425
Mana Restored: 20/27/34/41/48 per kill
Cost: 30/42/54/66/78 mana per second
Magic Damage: 30/50/70/90/110 (+0.20 per ability power)

Endgame items

Zhonya's Hourglass

+100 Ability Power
+45 Armor
UNIQUE Active - Stasis: Champion becomes invulnerable and untargetable for 2.5 seconds, but is unable to move, attack, cast spells, or use items during this time (90 second cooldown).

I would recommend the Crystal Scepter and Archangels Staff because you can then slow enemies with your e and with the staff you have almost infinite Mana and tons of ap (in combination with rod of ages about 150)